A) Field of the Invention
The present invention relates to a semiconductor device manufacture method, and more particularly to a semiconductor manufacture method by which a workpiece is processed by electron beam exposure.
B) Description of the Related Art
In manufacturing a semiconductor integrated circuit device, lithography is used to form a resist pattern by coating a resist layer on a workpiece layer and exposing and developing it. A precision of lithography is an important factor governing a precision, integration degree and the like of a semiconductor integrated circuit device.
Electron beam (EB) exposure has a high resolution and is suitable for micro processing in forming a pattern. EB exposure can draw a very thin pattern in a unit area of generally several μm, e.g., 4 μm at a maximum. EB exposure allows correction of alignment in a very fine unit.
If EB exposure is performed in a chip unit, as shown in FIG. 9A, alignment marks at four corners of a chip are detected, and a deflection and the like of an electron beam are aligned and exposure is performed. Alignment includes, along X- and Y-directions, contraction factors Gx and Gy, rotation Rx and Ry, trapezoid Hx and Hy, and translation Ox and Oy. The contraction factors Gx and Gy, rotation Rx and Ry, trapezoid Hx and Hy, and translation Ox and Oy can be obtained by matrix calculation shown in FIG. 9B, where (x, y) and (Δx, Δy) are position coordinate values and distortion coordinate values at each of chip four corners, respectively.
In detecting the position of an alignment mark of EB exposure alignment by detecting electrons reflected from the alignment mark, JP-A-HEI-9-36019 Publication proposes a method for raising an alignment mark detection precision by providing a plurality of detectors for reflected electrons and amplifiers and setting an amplification factor of each amplifier to make constant an output intensity.
In order to detect the position of an alignment mark at high precision and at high speed, JP-A-HEI-8-17696 proposes that electron beam scanning for detecting an alignment mark made of a step is performed by first scanning which scans a width larger than the width of the mark and second scanning which scans only the edges of the mark.
Detectors for reflected electrons and amplifiers are used for detecting reflected electrons. It cannot be said that a reflected electron signal is sufficiently strong. If noises are superposed upon the detectors, amplifiers and the like, a signal waveform is deformed, allowing an erroneous detection possibility.
If an erroneous detection occurs, an alignment precision will be lowered unless subsequent processes are corrected.